Fiber optic particle motion sensor and measuring method using the sensor

• US 8,240,207 B2
• Filed: 07/26/2011
• Issued: 08/14/2012
• Est. Priority Date: 10/16/2007
• Status: Active Grant

• Current Assignee: Avalon Sciences Ltd
• Original Assignee: Seismic Solutions Incorporated
• Inventors: Andersen, James K., Goldner, Eric Lee, Lam, Leo, Morey, William, Bush, Ira Jeffrey, Baker, Gerald, Cherbettchian, Agop
• Primary Examiner(s): Williams, Hezron E
• Assistant Examiner(s): Redmann, Gregory J
• Application Number:
  US13/190,516
• Publication Number:
  US 20110277548A1
• Time in Patent Office: 385 Days
• Field of Search: None
• US Class Current: 73/514.27
• CPC Class Codes: G01H 9/004 using fibre optic sensors light guides per se G02B6/00, acousto-optical devices specially adapted for gating or modulating in optical wave guides G02F1/125
• CPC Class Codes: G01P 15/093 by photoelectric pick-up
• CPC Class Codes: G02B 6/022 using mechanical stress, e.g. tuning by compression or elongation, special geometrical shapes such as "dog-bone" or taper G02B6/02204 takes precedence; optical modulation using photo-elastic effect G02F1/0131
• CPC Class Codes: G02B 6/29319 With a cascade of diffractive elements or of diffraction operations forming interferometer by splitting and recombining G02B6/29347 - G02B6/29358
• CPC Class Codes: G02B 6/29349 Michelson or Michelson/Gires-Tournois configuration, i.e. based on splitting and interferometrically combining relatively delayed signals at a single beamsplitter

Abstract

An optical sensor in which acceleration, acoustic velocity, or displacement (vibration) causes a corresponding shift in the center wavelength of the sensor output. The sensor can be coupled to a high-speed interferometric interrogator through an unbalanced fiber interferometer. The unbalanced interferometer functions to translate optical wavelength shift into phase shift, which is easily demodulated by the interrogator. A method of measuring acceleration uses the sensor.

Claims

1. A sensor comprising:

a housing;

a mass moveably disposed within the housing;

a first anchor attached to the housing;

a second anchor attached to the mass;

at least one suspension member interposed between the mass and the housing that allows the mass to move freely along one axis while restricting motions of the mass along all other axes, wherein the at least one suspension member includes at least one circular diaphragm and the at least one circular diaphragm contains at least one concentric ridge;

a section of an optical fiber attached at one end thereof to the first anchor and attached at the other end thereof to the second anchor, the section of optical fiber having a grating inscribed therein, the section of optical fiber serving both as a restoring spring and to sense relative motion between the mass and the housing;

an additional spring between the mass and the housing for imposing a fixed tension upon the fiber to enable measurements of motion of the sensor in any orientation; and

means for adjusting the spring to control the fixed tension imposed upon the fiber.

2. The sensor of claim 1 wherein the first anchor comprises a capstan.

3. The sensor of claim 1 wherein the second anchor comprises a capstan.

4. The sensor of claim 1 wherein the grating comprises a Bragg grating.

5. The sensor of claim 1 wherein the grating comprises a phase shifted grating.

6. The sensor of claim 1 wherein the grating comprises a pair of gratings comprising a Fabry-Perot interferometer.

7. The sensor of claim 1 wherein the grating has a central transmission peak.

8. The sensor of claim 1 wherein the grating has a transmission peak with a spectral width of approximately 0.3 picometers.

9. The sensor of claim 1 wherein the grating has a stop band of low transmission extending above and below a wavelength of the peak transmission.

10. The sensor of claim 1 wherein the grating has a stop bandwidth of approximately 1 nanometer.

11. The sensor of claim 1 wherein the mass is coupled to the housing by at least one flexible joint that allows free movement along one orthogonal axis and limits movement in the other two orthogonal axes.

12. The sensor of claim 11 wherein the at least one flexible joint comprises a circular diaphragm.